The present embodiments relate to medical diagnostic imaging. In particular, target information is identified by subtraction of background in medical diagnostic imaging.
Many cardiac interventions use real-time angiocardiogram imaging provided with a C-arm system. By rotating an X-ray source and detector on a C-arm, a 3D computed tomography (CT) volume may be reconstructed. Images may be generated from the volume.
A dynamic 3D model, such as a model of the left ventricle (LV), may be generated automatically from a rotational angiocardiogram. The model may be used to quantitatively evaluate cardiac function, such as LV volume, LV ejection fraction (EF) and regional wall motion during an intervention. The model may be used to provide visual guidance during an intervention by overlaying the model onto 2D fluoroscopy. The model may be used to reduce motion artifacts in 3D image reconstruction. The accuracy of the model may be determined by the segmentation of the target, which may be a challenging problem due to the overlapping of many confounding objects. For the LV, the descending aorta, bones, and diaphragm may be present in 2D projections. To improve the segmentation accuracy, the confounding objects may be removed.
Different approaches have been used to remove confounding objects in angiocardiograms. The target object (e.g., the LV) may have a large motion and the confounding objects (e.g., bones) may be static or have a smaller motion (e.g., the descending aorta). If the angulation of the C-arm is fixed (i.e., no translation and no rotation), a difference image is generated by subtracting the average image of adjacent frames in the image sequence. However, rotational motion of the angiocardiogram causes blurring using subtraction by adjacent frames.
Digital subtraction angiography (DSA) is another image enhancement technique. For each cardiac phase, two images are captured, one of the patient without injection of contrast agent and one of the patient with injected contrast agents. DSA is normally applied for a fixed C-arm angulation, but it is possible to apply this technique to rotational angiography. However, the C-arm is swept at least twice for acquiring images responsive to and not responsive to contrast agents. The longer acquisition time requires longer breath-holding by a patient, which may be difficult for a very sick patient, and may incur more radiation dose. Another challenge is synchronizing the C-arm motion and the cardiac motion to minimize the misalignment of the pre-contrast images and contrasted images.